1. Field of the Invention
The present invention relates generally to a reciprocating pump which may be pneumatically or electronically shifted.
2. State of the Art
Numerous industries and many applications utilize reciprocating pumps, particularly in the fluid industry. Reciprocating fluid pumps may include two fluid chambers. Each fluid chamber may include an associated pumping means, such as a piston, bellows, or diaphragm, which may be driven such that when one fluid chamber is being compressed to expel fluid, the other fluid chamber is expanded to receive fluid. The pumping means may include two pressure chambers, which alternate being filled with pressurized air and exhausting pressurized air. A reciprocating spool valve may operate the pumping means, shifting the pressurized air flow from one pressure chamber to the other as the pumping means reaches the end of a pumping stroke. A valve spool element in the spool valve may shift between two positions. The first position may supply pressurized air to the pressure chamber of one side of the pump while simultaneously exhausting the air from the pressure chamber on the other side of the pump. The shifting of the valve spool element simply alternates this pressurized air/exhaust between pressure chambers, driving the pumping means, thereby creating the reciprocating pumping action of the pump.
The valve spool element may be shifted mechanically, electronically, or pneumatically. A conventional, mechanically shifted reciprocating pump is described in U.S. Pat. No. 4,902,206 to Nakazawa et al. A system of rods and actuating means may drive the spool valve element to the opposite position each time the pumping means reaches the end of its pumping stroke, causing a new pumping stroke to begin. Pressurized air is thus supplied to alternating pressure chambers.
A conventional electronically actuated switching valve is described in U.S. Pat. No. 4,736,773 to Perry et al. An electronically actuated solenoid exhaust valve including pressure pilots on either side of a valve spool may be operable to cause a pressure drop in one pressure pilot on one side of the valve spool, causing the valve spool to change position.
A conventional pump which uses solenoids to regulate the supply of pressurized air between pressure chambers is described in U.S. Pat. No. 6,079,959 to Kingsford et al. Pressurized air may be injected into a pressure chamber, or the supply of pressurized air to a pressure chamber may be terminated when a fiber optic sensor senses the desired travel of a piston driving the pressure chamber.
A conventional pump having a pneumatically activated switching mechanism is described in U.S. Pat. No. 6,874,997 to Wantanabe et al. The switching mechanism of Wantanabe includes a rod having a bore formed in the axial direction extending from the base end to the tip. The bore has a top portion communicating with holes formed in the sidewalls. The holes in the sidewalls communicate with holes in a cylindrical case housing the rod when the rod is positioned in certain locations within the cylindrical case, namely near the end of a pump stroke. Pilot air or control fluid may pass through the bore within the rod, through the holes in the sidewall of the rod and the holes in the cylindrical case, and travel to a valve spool, causing the valve spool to change position, thereby switching the flow of pressurized air from one pressure chamber to the other. However, the bore and hole within the rod are difficult and expensive to manufacture, and lower the strength of the rod.
It may be desirable in some instances to use a pneumatic or mechanically actuated switching mechanism, while an electronically activated switching mechanism may be desirable in other applications. For example, electrical switching of the spool valve may be prohibited in some situations because of the potential for spark and fire hazards generally associated with electric (i.e., spark generating) switching devices.
A pump manufacturer may need to carry numerous parts to supply pneumatic, mechanical, and electronically controlled reciprocating pumps in order to meet the needs of different customers. Therefore, it would be advantageous to provide a pump system which requires only slight modification to be driven electronically or pneumatically.